05/06/2012 11:58 EDT | Updated 07/06/2012 05:12 EDT

London stages final test events ahead of Olympics

More than 40,000 spectators gathered Saturday night for a ceremony marking the official opening of London's new Olympic Stadium.

Nine-year-old Niamh Clarke-Willis from the London borough of Hackney was the lucky youngster selected to open the venue where the world's best athletes will compete for the 2012 London Olympics in July.

Organizers staged the final test events in the stadium earlier in the day for university students and disabled athletes.

By the evening, the crowd had grown in size to fill half the 80,000-seat stadium. Spectators cheered with the release of thousands of balloons.

"There was an impressive laser light show. It was an opportunity, really, for the public to get a first-hand look at the new Olympic Stadium," freelance journalist Dominic Valitis reported from London.

It was also a chance for officials to practise moving large crowds around the city's Olympic Park.

"It was a dry run for the people who will be running the stadium's management and security. All those who turned out last night, for example, had to get through airport-style security checks," Valitis said.

Overhead, police helicopters could be seen. On the ground, armed police were on patrol.

The 2012 London Olympic Games will run from July 27 to Aug. 12.